In a typical Swiss-type automatic screw machine, a plurality of cutting tools are radially disposed about a sliding headstock for cutting a workpiece which is rotatably and longitudinally driven relative to the tools. The cutting tools are typically comprised of a tool bit or insert attached to a tool holder or shank, and the shanks are selectively actuated to move the tools radially into and out of engagement with a workpiece to cut the workpiece as desired.
The tool shanks are typically made of rectangular-shaped bars which are slidably mounted within corresponding channels formed in a tool turret or gauge plate mounted around or above the headstock. The tool shanks are provided in the following industry-standard widths: 7 mm, 8 mm, 10 mm, 12 mm, 5/16 inch, and 1/2 inch. Most smaller automatic screw machines can accommodate only the 7 and 8 mm width shanks (referred to herein as "small-shank" cutting tools), whereas the larger automatic screw machines use the shanks having widths of 10 mm or larger.
Cutting tools having a shank width of 8 mm or larger are commercially available in several different configurations. In one type, the carbide tool bits are brazed to the ends of the shanks. In another type, interchangeable carbide tool inserts are screwed or clamped to the ends of the shanks. One advantage of the brazed cutting tools, is that they are relatively less expensive to manufacture and the tool bits are strongly secured in place. One advantage of the interchangeable tool inserts, on the other hand, is that the inserts are provided with more than one cutting edge so that when each edge becomes worn, chipped or otherwise requires replacement, the tool insert may be relatively quickly rotated or indexed on the shank by adjusting the fastener or clamp to position a fresh cutting edge of the insert into a cutting position. The clamping mechanisms may provide a secure lock; however, they are relatively bulky and may not always be easily mounted within the screw machines, particularly the machines requiring small-shank tools, and therefore may require additional set-up time and installation expense.
Currently, most cutting tool manufacturers provide the same series of tool inserts for use with each of the respective manufacturer's available shanks. In addition, most manufacturers only provide interchangeable tool inserts for tools having shank widths of 10 mm or larger. For cutting tools having shank widths of less than 10 mm, these manufacturers recommend the use of brazed tools, as described above. One drawback of the brazed tools, however, is that once the tool bits become worn, they must be ground to reform the cutting edges, or the entire tools must be replaced, and the machine must be reset to accept the re-ground tool. The inventor of this application is not aware of any manufacturer that has provided cutting tools with interchangeable inserts for shank widths of less than 8 mm, and he is aware of only one manufacturer that has provided cutting tools with interchangeable inserts for shank widths of 8 mm.
Referring to FIG. 1, a typical such commercially-available cutting tool is indicated generally by the reference numeral 1. The cutting tool 1 includes a rectangular-shaped shank 2 having a width of 8 mm, and a rhomboidal-shaped (or diamond-shaped) insert 3 attached to one end of the shank by a screw 4. As can be seen, the tool insert 3 is defined by an inscribed circle which is approximately equal to the width of the shank 2 (8 mm), and the shank defines a single tool-supporting edge 5 for engaging and supporting a corresponding edge of the tool insert. One of the problems encountered with this configuration is that if the insert is torqued in the clockwise direction in FIG. 1, the tool insert may become relatively easily dislodged on the shank, thus rendering the cutting tool ineffective and requiring time-consuming breakdown and set-up to either repair or replace the tool.
As illustrated in broken lines in FIG. 1, industry has attempted to overcome this problem by providing the shank with another, smaller supporting edge 5' on the opposite side of the tool insert relative to the first supporting edge 5. However, because of the size and location of the second supporting edge, it provides little additional support and has proven to break away relatively easily, and otherwise has failed to effectively prevent the insert from being dislodged when torqued in the clockwise direction in FIG. 1.
Accordingly, the prior art has failed to provide an acceptable small-shank cutting tool and interchangeable, rhomboidal-shaped tool inserts therefor, and it is an object of the present invention to provide such cutting tools and inserts therefor which overcome the drawbacks and disadvantages of the above-described prior art.